Titanium and titanium alloys have excellent corrosion resistance against chloride solution, and are broadly used as structural materials against seawater environments, chemical plants and others. On the other hand, crevice corrosion easily occurs in the chloride solution at high temperature, and this fact limits use of titanium materials. Ti-0.2%Pd alloy and Ti-0.8%Ni-0.3%Mo alloy have been developed in this respect (Japanese Patent Application Laid Open No. 130,614/75), are now utilized. However these titanium alloys are lower in strength than Ti-6Al-4V alloy which has been most widely used as high strength titanium alloy, and the titanium alloys are accordingly restricted with respect to application to parts requiring high strength.
Recently, studies have been made on high strength titanium alloy concerning the applications to oceanic developments, geothermal energy development, medical fields and so on. However, sometimes corrosion resistance is not excellent and examples of corrosion have been reported. In the medical field, titanium alloy is more satisfied with corrosion and stress corrosion resistant characteristics in the chloride environments than stainless steels and Co-Cr-Mo alloys, and further advantageously it does not contain harmful elements to human bodies such as Ni, Co and Cr. Now Ti-6 Al-4V (ELI) has been commercialized. But this kind of titanium alloy could not be satisfied with the corrosion resistance and corrosion-wear properties, and its toxicity in the human bodies is pointed out. The corrosion-wear properties is referred to concerning the wear of the material applied to hip prosthesis in the human bodies under the corrosion environment, and this characteristic is important in this kind of the application, since powders resulting from wear are harmful to the tissue of the human bodies. But titanium alloy is inferior in the wear resistant properties than stainless steel (SUS 316L) and Co-Cr-Mo alloy already used as the hip prosthesis.
U.S. Pat. No. 4,040,129 specifies elements to be contained in broad range, but it is found in examples that investigations are not made in detail and disclosures are insufficient with respect to the hot workability, the corrosion-wear property and the characteristics of the human body in the corrosion circumstances.
As seen from the above, in the conventional titanium alloy, the corrosion resistance could be improved in Ti-0.2Pd alloy and Ti-0.8Ni-0.3Mo alloy, while the strength is still required. On the other hand, the corrosion resistance and the corrosion-wear properties are inferior in Ti-6Al-4V (ELI) of the high tensile titanium alloy.
The present invention has been conducted in view of the existing problems, and it is an object of the invention to provide a high strength and corrosion resistant titanium alloy which has the equivalent strength to that of Ti-6Al-4V (ELI) alloy and especially which could well satisfy the corrosion-wear property and suitability to the human body.